Device for alternating-current-motor control.



PATENTED NOV. 17, 1903.

J. LE 0. DAVIS.

DEVICE FOR ALTERNATING CURRENT MOTOR CONTROL.

APPLICATION FILED JULY 22, 1903.

N0 MODEL.

7 INVENTOR. Joseph L. C. Dczvi S,

WITNESSES ATTORNEY.

UNITED STATES Patented November 17, 1903.

Patent OFFICE.

JOSEPH LE CONTE DAVIS, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERALELECTRIC COMPANY, A CORPORATION OF NEW YORK.

DEVICE FOR ALTERNATlNG=tC URRENT-MOTQR CONTROL.

SiEGIFIGATIGN forming part of Letters Patent No. 744,053, datedhi'ovember 17, 1 0

Application filed July 22, 1908. Serial No. 166,570. (No modelf;

To all whom it may concern.-

Be it known that I, Josnrn Ln Gonrn DAVIS, acitizen of the UnitedStates, residing at Schenectady, in the county of Schenectady and Stateof New York, have invented certain new and useful Improvements inDevices for AlternatingCurrent-Motor Control, of which the followingis aspecification.

My invention relates to the control of alterhating-current motors; andits object is to provide means for the operation of such motors at anyspeed and for obtaining uniform acceleration from rest to full speedwith maximum torque over the entire range. Furthermore, by means of myinvention phase compensation can be obtained, so that the motors willoperate at a high-power factor throughout their entire range of speed.Furthermore, my invention is adapted to the control of a number ofmotors from one point, and therefore is especially suited to the controlof a plurality of motors on the several cars of a train.

Referring to the drawings, Figure 1 shows an arrangement embodying myinvention, and Figs. 2 and 3 are explanatory diagrams of the same.

Referring first to Fig. 2, S S represent the stators of twoalternating-current motors. The motors are shown as of the three-phasetype; but myinvention is not limited to any particular number of phases.It is applicable to motors of single phase or of any number of phases.The stators S S are excited from the leads 1, 2, and 3. E F, representthe rotors of the two motors. Three-phase taps are led off from eachrotor, and the two rotors are connected by the secondary leads 4:, 5,and 6. If the motors are symmetrical in winding and if the rotors aresimilarly placed, with the rotor-taps occupying the same relativepositions as indicated by the full-line triangles in Fi 2, it is evidentthat the electromotive force generated in each phase of each motor willbe opposed in the secondary leads t 5 6 by an equal and oppositeelectromotive force generated by the rotor of the other motor.Consequently no current can flow, and there will be no tendenoy for themotors to turn. If, new, either of the rotors is displaced, asindicatedby the dotted triangles in Fig. 2, the electromotive forcegenerated in the different phases of the different. motors will be nolonger equal and opposite and a strong synchronizing-cur- 5 rent willflow between the rotors, which will tend to restore the rotors to thesame relative positions. It is evident that if the contactpoints of therotors could be maintained stationary in space,with one rotor displacedrelative to the other, a constant torque would be developed and therotors would revolve at a certain speed, dependent upon the load. Thisobject would be attained by means of a commutator and brushes. if eachrotor is supplied with a commutator, the contact-points will be fixed bythe position of the brushes, and by displacing the two sets of brushesrelatively to each other a constant torque will be obtained. it isevident that the direction of rotation of the motors will depend uponthe direction in which the brushes are relatively displaced.Furthermore, the amount of synchronizingourrent and consequent torquewill depend upon the amount of relative displacement of the brushes.Thus the direction of rotation and the amount of torque, andconsequently the speed, may be controlled by the shifting of thebrushes. It is evident, however, that one of the rotors will revolve inthe opposite direction to that of the rotating field, while the otherrotor will revolve in the same direction its rotating field. Thevoltages developed in the two rotors will therefore be unequal, and awattless magnetizing-current will fiow between the rotors in addition tothesynchronizing-current. Thismagnetizingcurrent reacting on the primarycurrents in the stators will produce a distortion of the phase of theprimary currents; but if the amount and phase of current-flow betweenthe two motors is properly controlled the reaction of the rotor-currentsupon the primaries may be made to diminish the magnetizingcurrent of theprimaries, and consequently to increase the power factor at which thesystem operates. Fig. 3 shows diagrammatically the means for thuscontrolling the current flowing between the rotors. If the rotors aresymmetrically disposed, as before, equal voltages will be developed andno current can flow in the secondary leads 4 5 6 due to the rotor voltages. If, however, boosters F F F are inserted in the secondary leadsat 5 6 and are excited, it is evident that current will flow through therotors in relatively opposite directions in the two and that rotationwill be produced in the same directions as if the brushes had beenshifted. The torque, and consequently the speed, will depend upon theamount of the booster voltage.

I thus have two means of controlling the speed of the rotors and thecurrent-flow between them. By properly proportioning the booster voltageand the relative shifting of the brushes I am able to obtain not only agradual acceleration in speed with large torque, but also compensationfor the primary magnetizing-current. Such an arrangement is shown inFig. 1. S S represent the stators and R R the rotors of the two motors.Oarried by the rotors are the commutators O O, on which bear the twosets of brushes B B and B B. The two sets of brushes are con' nected bythe secondary leads 4 5 6. D D represent the holders for brushes B B.These holders are rotatably mounted as regards commutators O C. E is alever by means of which the brush-holders and brushes may be relativelyshifted. G G G represent switches actuated by the movement of lever Eand adapted to vary the excitation of the boosting-coils F F F. Theoperation of this arrangement will be evident from the foregoingexplanation. It is not necessary that both stators should be excitedfrom the mains. One stator may be short-circuited on itself and receiveits exciting current from its rotor. It is obvious that either stator orrotor may be provided with a commutator and receive the varyingvoltages. The use of stator and rotor interchangeably is well known inthe art. Such modification requires no additional explanation byillustration.

Obviously the boosting-coils for a number of sets of motors may beconnected in series or in parallel and their excitation controlled fromone point. Furthermore, the levers of a number of pairs of motors may beoperated synchronously from one point by means of any well-known form ofapparatus adapted for synchronous movement. Many forms of such devicesare well known in the art and require no description here. Thus myinvention is particularly applicable to alternatingcurrent traincontrol.

I do not desire to limit myself to the particular construction andarrangement of parts here shown, since changes therein which do notdepart from the spirit of my invention and which are within the scope ofthe appended claims will be obvious to those skilled in the art.

What I claim as new, and desire to secure by Letters Patent of theUnited States, is

1. In combination, two alternating-current motors, the winding of onemember of each of said motors being supplied with a commutator, a closedcircuit including said windings, and means for producing in said circuita current varying simultaneously in magnitude and phase.

2. In combination, two altemating-current motors, the winding of onemember of each motor being supplied with a commutator, a closed circuitincluding said windings, and means for controlling the amount and phaseof the current in said circuit.

3. In combination, two motors, means for producing a varying magneticllux in one member of each motor, a commutator carried by the othermember of each motor, a set of brushes bearing on each commutator, leadsconnecting said sets, means for shifting one set relative to the other,and means for producing variable voltages in said leads.

a. In combination, two alternating-current motors, of the commutatortype, leads connecting the brushes on one motor to the brushes of theother motor, means for producing variable voltages in said leads, andmeans for shifting the brushes of said motors.

5. In combination, two alternating-current motors, a commutator for eachmotor, a set of brushes bearing on each commutator, leads connectingsaid sets, a brush-shifting device, and means for producing variablevoltages in said leads.

6. In combination, two alternating-current motors, a commutator for eachmotor, a set of brushes bearing on each commutator, leads connectingsaid sets, a brush-shifting device, and booster-coils inserted in saidleads.

7. In combination, two alternating-currcnt motors of the commutatortype, leads connecting the brushes of one motor to the brushes of theother motor, booster-coils in said leads, and a brush-shitting device.

8. In combination, two alternatirig-current motors of the commutatortype, means for producing a varying magnetic flux in one member of eachmotor, a closed circuit including the windings of the other members ofsaid motors, and means for controlling the amount and phase of thecurrent in said circuit.

9. In combination, two alternating-current motors having commutators andbrushes, leads connecting like brushes of the two motors, means forrelatively displacing the brushes of one motor, and means forcontrolling the amount and phase of the current in said leads.

10. In combination, two alternating-current motors having commutatorsand brushes, leads connecting like brushes of the two motors, and meansfor producing in said leads currents varying simultaneously in magnitudeand phase.

In witness whereof I have hereunto set my hand this 20th day of July,1903.

JOSEPH LE CONTE DAVIS.

Witnesses:

BENJAMIN B. HULL, HELEN .ORFORD.

